A need exists to provide better, more finely controlled conductive polymers with tailored endgroups for use in block copolymer synthesis, utilization in nanofabrication, and general commercial exploitation in electronic and semiconducting devices including photovoltaic and light emitting diode applications.
Regioregular conductive polymers including polythiophenes are of particular importance. Due to their excellent electrical properties, regioregular polythiophenes are rapidly being developed into new commercial products with applications ranging from transistors to hole-transport layers in organic light-emitting diodes (OLEDs) to new specialty plastics. See, for example, Kline et al., Adv. Mater. 2003, 15, 1519; Brown et al., Science 1995, 270, 972; Sirringhaus et al. Nature 1999, 401, 685; Sirringhaus et al. Science 1998, 280, 1741; Huynh et al. Science 2002, 295, 2425; Bao et al. Appl. Phys. Lett. 1996, 69, 3; McCullough et al. J. Org. Chem. 1993, 58, 904; Chen et al. J. Am. Chem. Soc. 1995, 117, 233; and R. S. Loewe et al. Adv. Mater. 1999, 11, 250.
As regioregular polythiophenes grow in importance, so does the development of inexpensive and convenient methods for the synthesis of these polymers. Work has been reported for the modification and variation of side chains of regioregular, head-to-tail coupled polythiophenes (HT-PTs). See, for example, McCullough, Adv Mater. 1998, 10, 93. Less attention has been given to the nature and control of end groups of such polymers. Procedures published to date to functionalize end groups of conjugated polymers are limited in scope and number. See, for example, Liu et al. Macromolecules 2002, 35, 8; Langeveld-Voss et al. Chem. Commun. 2000, 2000, 81; Jayakannan et al. Macromolecules 2001, 34, 8; Iraqi et al. J. Mater. Chem. 1998, 8, 25.
Previously, it has been reported a multistep synthesis of HT-PTs bearing amino and hydroxyl groups. See, for example, Liu et al. Macromolecules 2002, 35, 8. The hydroxylated PTs were further derivatized and used to synthesize, e.g., HT-PT-polystyrene diblock and triblock copolymers. See, for example, J. Liu et al. Angew. Chem. Int. Ed. 2002, 41, 4. These copolymers can self-assemble into nanowires, resulting in surprisingly high conductivities, even with relatively low percentages of HT-PT in the copolymer. Despite these advances, new convenient synthetic methods are needed that are simple and reproducible and involve fewer numbers of synthetic steps.
In addition, U.S. Pat. No. 6,602,974 to McCullough et al. describes one system of block copolymers prepared by use of tailored endgroups. The '974 patent describes use of Grignard reagent to treat a regioregular polythiophene polymer. Also, U.S. Pat. No. 6,166,172 to McCullough et al. describes an improved method for synthesis of conducting polymers including larger scale methods.
Despite these advances, additional synthetic versatility and precision is needed. In particular, it is important to control whether one or both ends of the polymer chain are functionalized. New routes to block copolymers are needed as well as block copolymers having better processability and conductivity.